The present invention is directed to a metal-promoted zeolite beta catalyst
useful in the selective catalytic reduction of nitrogen oxides with
ammonia in which the zeolite beta is pre-treated so as to provide the
zeolite with improved hydrothermal stability.
The stabilized beta zeolite is provided by incorporating into the zeolite
structure non-framework aluminum oxide chains. The aluminum oxide chains
can be incorporated into the zeolite structure by a unique steaming
regimen or by treatment with rare earth metals, such as cerium. The
treatment process is unlike well-known methods of dealuminizing zeolites
for the purpose of increasing the silica to alumina ratio. In the present
invention, the non-framework aluminum oxide is characterized by FT-IR by a
peak at 3781.+-.2 cm.sup.-1, which when present, stabilizes the zeolite
against further dealumination such as under oxidizing and harsh
hydrothermal conditions.
